INJECTION 235 



521. Robin's Prussian Blue Colouring Mass {ibid., p. 35, and 

 2nd ed., p. 1013). 



Take— 



(a) Ferrocyanide of potassium (sol. sat.) . . 90 c.c. 

 Glycerin . . . . . . 50 ,, 



(b) Solution of ferric chloride at 30° Baume . 3 ,, 

 Glycerin . . . . . . 50 ,, 



Mix slowly and combine the mixture with 3 parts of vehicle. 

 It is well to add a few drops of HCl. 



CARMINE-GELATIN MASSES 



522. Ranvier's Carmine-Gelatin Mass [Traite technique, p. 

 116). Take 5 grm. Paris gelatin, soak until quite swollen and 

 soft, wash, drain and melt it in the water it has absorbed over a 

 water-bath. When melted add slowly, and with continual agita- 

 tion, 2h grm. of carmine rubbed up with a little water, and just 

 enough ammonia, added drop by drop, to dissolve the carmine 

 into a iranspcirent solution. 



The mixture is now neutralised by adding cautiously, drop 

 by drop, with continual agitation, a solution of 1 part of glacial 

 acetic acid in 2 parts of water. (When the mass is near neutrality, 

 dilute the acetic acid still further.) The instant of saturation is 

 determined by the smell of the solution, which gradually changes 

 from ammoniacal to sour. As soon as the sour smell is perceived 

 the liquid must be examined under the microscope. If it contains 

 a granular precipitate of carmine, too inuch acid has been added, 

 and it must be thrown away. 



The mass, having been perfectly neutralised, is strained through 

 new flannel. 



523. How to Neutralise a Carmine Mass (Ville, Gaz. hebd. d. 

 Sci. vied, de Montpellier, Fev., 1882). Ville points out that 

 when carmine is treated with ammonia a certain proportion of 

 the ammonia combines with the carmine and the rest remains 

 in excess. It is this excess that it is required to neutralise pre- 

 cisely, not the whole of the ammonia employed. 



To neutralise the acidity of commercial gelatin, it should be 

 washed for an hour or so in running water. 



As to the neutralisation of the colouring mass Ville is of 

 opinion that the sour smell cannot be safely relied on in practice, 

 and prefers to employ dichroic litmus paper (litmus paper sen- 

 sitised so as to be capable of being used equally for the demon- 

 stration of acids and bases). For directions for preparing this 

 see loc. cit. or previous editions. 



524. Hover's Carmine- Gelatin Mass {Biol. Centralb., 1882, 

 p. 21). Take a concentrated gelatin solution and add to it the 



